plněnou nano TiO2
Disertační práce
Studijní program: P3106 – Textile Engineering
Studijní obor: 3106V015 – Textile Technics and Materials Engineering Autor práce: Bandu Madhukar Kale
Vedoucí práce: prof. Ing. Jiří Militký, CSc.
Liberec 2017
Loaded Cellulose
Dissertation
Study programme: P3106 – Textile Engineering
Study branch: 3106V015 – Textile Technics and Materials Engineering
Author: Bandu Madhukar Kale
Supervisor: prof. Ing. Jiří Militký, CSc.
Liberec 2017
Byl jsem seznámen s tím, že na mou disertační práci se plně vztahuje zákon č. 121/2000 Sb., o právu autorském, zejména § 60 – školní dílo.
Beru na vědomí, že Technická univerzita v Liberci (TUL) nezasahuje do mých autorských práv užitím mé disertační práce pro vnitřní potřebu TUL.
Užiji-li disertační práci nebo poskytnu-li licenci k jejímu využití, jsem si vědom povinnosti informovat o této skutečnosti TUL; v tomto pří- padě má TUL právo ode mne požadovat úhradu nákladů, které vyna- ložila na vytvoření díla, až do jejich skutečné výše.
Disertační práci jsem vypracoval samostatně s použitím uvedené lite- ratury a na základě konzultací s vedoucím mé disertační práce a kon- zultantem.
Současně čestně prohlašuji, že tištěná verze práce se shoduje s elek- tronickou verzí, vloženou do IS STAG.
Datum:
Podpis:
iv
DECLARATION
I hereby declare that the material in this thesis, herewith I now submit for assessment for PhD defence is entirely my own work. I have taken precautionary measures to ensure that the work is original and does not to the best of my knowledge breach any copyright law, and hasn’t been extracted from the work of others save and to the extent that such work has been cited and acknowledged within the text of this work.
The core theme of the thesis is Multifunctional cotton fabric with nano TiO2 loaded cellulose and contains 5 original papers published in peer reviewed impact factor journals, 1 book chapter and 5 papers presented in international conferences. The ideas, development and writing up of all the papers in the report were the principal responsibility of me, the candidate working within the Department of Material Engineering, under the supervision of prof. Ing.
Jiří Militký, CSc, EURING.
Name: Mr. Bandu Madhukar Kale, M.Sc.
Signature:
Student Number: T13000168 Liberec, March 2017
v
TABLE OF CONTENT
DECLARATION
... ivACKNOWLEDGEMENTS
... viiiABSTRACT
... ixABSTRAKT
... xiLIST OF FIGURES
... xiiiLIST OF TABLES
... xviLIST OF ABREVIATIONS
... xviiLIST OF UNITS
... xviiiCHAPTER 1 INTRODUCTION
... 11.1 Background ... 1
1.2 Research problem ... 2
CHAPTER 2 AIM AND OBJECTIVES
... 5CHAPTER 3 LITERATURE REVIEW
... 63.1 Cotton ... 6
3.2 Functional fabric ... 6
3.3 Self-cleaning materials ... 7
3.4 Antibacterial cotton fabric ... 9
3.5 Antifungal cotton fabric ... 11
3.6 Stiff cotton fabric ... 12
3.7 Functional nanoparticles ... 13
3.7.1 Titanium dioxide ... 15
3.7.2 Uses of Titanium dioxide ... 16
3.7.3 Photoinduced hydrophilicity by generation of light induced surface ... 18
3.7.4 Mechanism of self-cleaning and antimicrobial by Titanium dioxide ... 20
3.7.5 Methods to apply Titanium dioxide ... 21
vi
3.8 Starching ... 21
3.9 Cellulose ... 23
3.10 Cellulose-TiO2 coating ... 24
3.11 Solvents for cellulose dissolution ... 25
CHAPTER 4 EXPERIMENTAL
... 284.1 Materials ... 28
4.2 Cellulose coating ... 29
4.2.1 Cellulose dissolution ... 29
4.2.2 Dispersion of TiO2 nanoparticles in cellulose solution ... 29
4.2.3 Padding ... 30
4.3 Dyeing with reactive dyes ... 31
4.4 Charactrization and measurements ... 32
CHAPTER 5 RESULTS AND DISCUSSION
... 415.1 Morphology of cellulose and cellulose-TiO2 coated cotton fabric ... 41
5.2 Photocatalytic degradation of orange II under UV light ... 43
5.3 Wine stain degradation ... 44
5.4 Durability of cellulose coated cotton fabric for self-cleaning ability ... 46
5.5 Rubbing effect on wine stain degradation ... 47
5.6 Stiffness ... 48
5.6.1 Stiffness of cellulose coated cotton fabric in Urea-Thiourea-NaOH ... 48
5.6.2 Stiffness of cellulose-TiO2 coated cotton fabric in 60% Sulfuric acid ... 51
5.7 Durability of stiffness against washing of cellulose-TiO2 coated cotton fabric .... 52
5.8 Antibacterial activity of cellulose-TiO2 coated cotton fabric... 53
5.9 Evaluation of Antifungal activity of cellulose-TiO2 coated cotton fabric ... 57
5.10 Investigation the effect of cellulose-TiO2 coating and strong solvent on cellulose structure by X-ray diffraction patterns ... 59
5.10.1 Effect of cellulose-TiO2 coating and 60% Sulfuric acid on structure of cellulose ... 59
5.10.2 Effect of NaOH-Urea-Thiourea solvent system on cellulose structure ... 62
5.11 Colur strength and related parameter ... 65
5.12 Evaluation of fastness properties ... 67
vii
5.13 Mechanical properties ... 70
5.14 Air and water vapor permeability ... 71
CHAPTER 6 CONCLUTIONS
... 736.1 Morphology and X-ray diffraction ... 73
6.2 Photocatalytic self-cleaning ... 73
6.3 Stiffness ... 74
6.4 Antibacterial and antifungal activity... 74
6.5 Mechanical and comfort properties ... 74
6.6 Dyeing ... 74
CHAPTER 7 APPLICATIONS AND FUTURE WORK
... 75REFERENCES
... 78LIST OF PUBLICATIONS
... 90
viii
ACKNOWLEDGMENTS
First and foremost, I would like to express my sincere respect and appreciation to my supervisor Prof. Ing. Jiri Militky, CSc. EURING, for his inspiration, guidance and giving me an opportunity to work under his kind supervision. I want to say special thanks to Prof. Ing. Jakub Wiener, PhD for his time-to-time suggestions and help during my entire research work. He has been encouraging and supportive throughout my entire time at Technical University of Liberec, and I would like to thank doc. Rajesh Mishra, PhD for his kind help and support during my entire study. In the absence of financial support, this research would not have been possible; I, therefore, thank Ing. Jana Drasarova, Ph.D (Dean of the Faculty of Textile Engineering); Ing.
Gabriela Krupincova, PhD (Vice-Dean for Science and Research), Ing. Pavla Tesinova, PhD (Vice-Dean for international affairs) and Dr. Blanka Tomkova (HOD, Department of Materials Engineering) for their kind support, conference attendance and mobility funds where necessary such that this work may be done and progresses to another level.
For crystal structure analysis, there was a need of X-ray diffraction (XRD) patterns and I am grateful to Prof. Youjiang Wang, Dr Thomas Oomman, Dr David Tavakoli and Prof. Karl Jacob for providing chemicals, testing facility and their help during my internship stay at School of Material Science and Engineering Georgia Institute of Technology, Atlanta, USA.
I would like to say a big thank you to my work colleagues in the department especially Samson Rwawiire and Abdul Jabbar who we always shared the perils of doctoral research. I would also like to thank Ing. Hana Cesarová Netolická, Kateřina Štruplová, Ing. Hana Musilová, Bohumila Keilová, Martina Čimburová and Jana Grabmüllerová for their regular help and support. I want to say special thanks to Dr Anasuya Sahoo for her constant support and guidence in my personal and professional carrier.
Finally yet importantly, where I am today is only because of the prayers of my parents and best wishes of brothers, sisters, uncles, aunts, sister in-laws, nieces and nephew.
Bandu Madhukar Kale
ix
ABSTRACT
Cotton is a leading textile fibre due to its unique properties such as hydrophilicity, biodegradability, durability, good dyeability, and relatively low cost. However, now a day’s people want cotton fabric to be smart, which can give comfort according to weather conditions.
Self-cleaning, antibacterial, antifungal and permanently stiff textiles are becoming important due to market demand, and broad research is being done in this areas. Nanoparticles such as Titanium dioxide (TiO2), Zinc oxide (ZnO), Copper oxide (CuO), Silver (Ag), Carbon nanotubes (Singlewalled carbon nanotubes (SWCNTs), Multiwalled carbon nanotubes (MWCNTs) show excellent functional activity towards light. Nano TiO2 is the most environment-friendly and relatively cheap among all other nano particles. TiO2 can be applied on different substrates such as activated carbon, stainless steel and glass. Researchers have coated TiO2 on cotton fabric by various methods such as in-situ suspension polymerization with nano TiO2-acrylatecopolymer and functionalizing cotton fabric with nano sized TiO2.
However, they do not claim that fabric is stable against washing.
In this thesis, a new route to make cotton fabric self-cleaning and permanently stiff by coating cellulose-TiO2 on its surface is demonstrated. Cellulose solution was prepared by dissolving 10% cellulose in aqueous sulphuric acid (60%) or Sodium hydroxide-Urea-Thiourea solvent system. TiO2 with different concentrations (1, 3, 5 and 10 % TiO2 on the weight of cellulose) was dispersed in cellulose solution and coated on the surface of cotton fabric by padding machine. The surface morphologies of pure cotton fabric, cellulose and cellulose-TiO2 coated cotton fabric were observed on scanning electron microscope (SEM). Simulation method was developed to quantify amount of cellulose II by using X-ray diffraction patterns on Mercury software. Effect of cellulose coating on dyeing was investigated with Reactive dyes.
Self-cleaning ability of cellulose-TiO2 coated cotton fabric was investigated with Orange II dye and wine stain under UV light. Antibacterial and antifungal activity was studied according to international standards. Results revealed that samples coated with more than 3% TiO2 showed strongest inhibition efficiency against Staphylococcus aureus (SA), Methicillin resistant Staphylococcus aureus (MRSA) bacteria’s. Antifungal testing results showed that the photo-catalytic activity of titanium dioxide nanoparticles allows a disinfection of cotton fabric from fungal colonization. The amount of cellulose II in cotton fabric increased slightly after solvent treatment. However, breaking strength also increased by cellulose coating. Air and water vapor permeability were hardly affected. The stiffness of cellulose coated cotton fabric increased substantially. Degradation of orange II dye was increased with increasing TiO2
x concentration and irradiation time. The samples coated with 1, 3 and 5% TiO2 were stable against washing up to 20 washing cycles for both self-cleaning and stiffness properties.
However, 10% TiO2 coated sample does not show similar stability against washing due to poor dispersion of TiO2 in cellulose solution.
Keywords: Cotton fabric, cellulose, self-cleaning, stiffness, antibacterial, antifungal, Titanium dioxide.
xi
ABSTRAKT
Bavlna je díky svým jedinečným vlastnostem jako je hydrofilita, biodegradabilita, trvanlivost, dobrá barvitelnost a relativně nízká cena významným textilním materiálem. Dnes však lidé očekávají od bavlněné tkaniny i další vlastnosti, díky nimž poskytuje bavlna komfort podle počasí. Vzhledem k požadavkům trhu roste význam samočisticích, antibakteriálních, antimykotických a nemačkavých textilií, které jsou předmětem rozsáhlého výzkumu.
Nanočástice jako TiO2, ZnO, oxid měďnatý, Ag nebo uhlíkové nanotrubice (SWCNTs nebo MWCNTs) vykazují vynikající funkcionalizační aktivitu na světle. Nanočástice oxidu titaničitého jsou nejšetrnější k životnímu prostředí a ve srovnání s ostatními nanočásticemi i relativně levné. TiO2 lze aplikovat na různé substráty jako je aktivní uhlí, nerezová ocel nebo sklo. Výzkumníci aplikují TiO2 na bavlněné tkaniny různými způsoby, jako je in situ suspenzní polymerace s nano TiO2-akrylátovým kopolymerem a funkcionalizace bavlněné tkaniny nanočásticemi TiO2. Nicméně tyto tkaniny nejsou odolné v praní.
Tato práce se zabývá přípravou samočisticí ztužené bavlněné tkaniny potažené celulózou a TiO2.. Celulózový roztok se připraví rozpuštěním 10% celulózy ve vodném roztoku 60%
kyseliny sírové a nebo v rozpouštěcí směsi z hydroxidu sodného, močoviny a thiomočoviny.
TiO2 o různých koncentracích (1, 3, 5 a 10% TiO2 z hmotnosti celulózy) se disperguje v roztoku celulózy a nanese na povrch bavlněných tkanin klocováním. Povrchová morfologie čisté bavlněné tkaniny a bavlněné tkaniny povrstvené celulózou a celulózou s TiO2 byla pozorována rastrovacím elektronovým mikroskopem (SEM). Pro kvantifikaci celulózy II byla vyvinuta simulační metoda s použitím rentgenové difrakce na softwaru Mercury. Vliv celulózového povrstvení na barvitelnost byl zkoumán pomocí reaktivních barviv.
Samočisticí schopnost bavlněné tkaniny potažené celulózou a TiO2 byla zkoumána pomocí barviva Orange II a skvrn od vína pod UV světlem. Antibakteriální a protiplísňový účinek byl testován podle mezinárodních norem. Výsledky ukázaly, že vzorky potažené více než 3% TiO2 vykazovaly nejsilnější inhibiční účinek na bakterie Staphylococcus aureus (SA) a methicillinu rezistentní Staphylococcus aureus (MRSA). Protiplísňové testy ukázaly, že fotokatalytická aktivita nanočástic oxidu titaničitého umožňuje dezinfikovat bavlněnou tkaninu od kolonií plísní. Množství celulózy II v bavlněné tkanině se po ošetření rozpouštědlem mírně zvýšilo.
Celulózový povlak také zvýšil pevnost do přetrhu bavlněné tkaniny. Prodyšnost a paropropustnost prakticky nebyly ovlivněny. Tuhost bavlněné tkaniny potažené celulózou se podstatně zvýšila. Degradace barviva Orange II se zvyšuje s rostoucí koncentrací TiO2 a dobou ozařování. Pokud jde o tuhost i samočisticí vlastnosti, vzorky potažené 1, 3 a 5% TiO2 byly
xii odolné v praní do 20 pracích cyklů. Nicméně vzorek potažený 10% TiO2 nevykazoval podobnou stabilitu v praní v důsledku špatné dispergovatelnosti TiO2 v roztoku celulózy.
Klíčová slova: bavlněná tkanina, celulóza, samočištění, tuhost, antibakteriální, protiplísňový, oxid titaničitý
xiii
LIST OF FIGURES
Figure 1 Figure 1. Cotton bolls ready for harvest 6
Figure 2 Figure 2. Functional fabric 7
Figure 3 Lotus effect 8
Figure 4 Functional nanomaterials a) Copper oxide b) Titanium dioxide c) Zinc oxide d) Silver oxide e) Single-walled carbon nanotube f) Multi-walled carbon nanotube
14
Figure 5 Forms of Titanium dioxide 15
Figure 6. Schematic illustration of various processes occurring after photoexcitation of pure TiO2 with UV light
17
Figure 7 Schematic representation of photo-induced hydrophilicity.
Electrons reduce the Ti(IV)–Ti(III) state and thereby the oxygen atoms will be ejected (creation of oxygen vacancies). Oxygen vacancies will increase the affinity for water molecules and thereby transforming the surface hydrophilic
19
Figure 8 Mechanism of self-cleaning, antibacterial and antifungal by TiO2 20
Figure 9 Representative partial structure of amylose 22
Figure 10 Representative partial structure of amylopectin 22
Figure 11. Chemical structure of cellulose 24
Figure 12 Graphical representation of cellulose-TiO2 coating. 25 Figure 13 Chemical structure of (a) Cellulose xanthate (b) Cellulose
carbamate (c) Cellulose acetate and (d) Methyl cellulose
26
Figure 14 Chemical structure of (a) Ionic liquid and (b) N-methyl morpholine N-oxide
27
Figure 15 Cotton fabric used for study 28
Figure 16 Dissolution and dispersion of TiO2 29
Figure 17 Padding machine 30
Figure 18 TS5130 Vega-Tescan Scanning Electron Microscope 32 Figure 19 PANalytical X'Pert³ X-ray powder diffractometer 33 Figure 20 Method to analyze photocatalytic degradation of stain by ImageJ 35
Figure 21(a) Device TH-7 36
Figure 21(b) Hysteresis loop of bending from device TH-7 37
xiv Figure 22. Scheme and photography of bending sample on device TH-7 37 Figure 23 SEM images of (a, c) uncoated cotton fabric and (b, d) cellulose-
coated cotton fabric
41
Figure 24 SEM photographs of TiO2 - cellulose coated cotton fabric a) Control, b) 0% TiO2, c) 1 % TiO2, d) 3% TiO2, e) 5 % TiO2, f) 10% TiO2
42
Figure 25 Degradation of Orange II under UV-visible light irradiation on cellulose-TiO2 coated samples
43
Figure 26 Evaluation of orange II degradation by ImageJ 44
Figure 27 Scanned pictures of (a) Control (b) only cellulose coated and (c) TiO2-cellulose coated cotton fabric after irradiation of red wine stain under UV light
45
Figure 28 Effect of TiO2 concentration on wine stain degradation 45
Figure 29 Effect of washing on stain degradation 46
Figure 30 Scanned images of wine stain degradation of rubbed samples after 15 minuts of UV irradidition
47
Figure 31 Evaluation of rubbing effect on wine stain degradation after 15 min of UV irradiation by ImageJ
48
Figure 32 Stiffness of uncoated and coated samples 49
Figure 33 Effect of cellulose concentration on stiffness of cotton fabric 50 Figure 34 Durability of only cellulose coated cotton fabric against washing 50 Figure 35 Stiffness of control, Solvent treated (Sol. Tr.), Starched, only
cellulose (0% TiO2) and cellulose-TiO2 coated cotton fabric.
52
Figure 36 Durability of stiffness against washing 53
Figure 37(a) Antibacterial activity against Staphylococcus aureus bacteria 54 Figure 37(b) Antibacterial activity against Methicillin-resistant Staphylococcus
aureus
55
Figure 38 Antifungal activity of (a) Control (b) 1% TiO2 (c) 3% TiO2 (d) 5%
TiO2 and (e) 10 % TiO2 coated cotton fabric
58
Figure 39 X-ray diffraction patterns of cellulose-TiO2 coated cotton fabric 60 Figure 40 Diffraction pattern of Control (red curve) and solvent (without
cellulose) treated (blue curve) cotton fabric
60
xv Figure 41 Diffraction pattern of control cotton fabric fitted with simulated
pattern
61
Figure 42 Diffraction pattern of 60 % H2SO4 treated cotton fabric fitted with simulated pattern
61
Figure 43 X-ray diffraction pattern and analysis of original (Black) and regenerated (Red) cellulose pulp.
63
Figure 44 X-ray diffraction pattern and analysis of control (black) and solvent treated cotton fabric (Red).
63
Figure 45 Diffraction pattern of control cotton fabric fitted with simulated pattern.
64
Figure 46 Diffraction pattern of solvent treated cotton fabric fitted with simulated pattern
64
Figure 47 Breaking strength of control, Solvent treated (Sol. Treat.) and coated cotton fabrics.
70
Figure 48 (a) Effect of cellulose-TiO2 coating on air permeability of cotton fabric
71
Figure 48 (b) Effect of cellulose coating on water vapor permeability of cotton fabric
72
Figure 49 Cellulose-TiO2 coated cotton fabric self-cleaning applications 75
Figure 50 Stiff fabric applications 76
Figure 51 Antibacterial and antifungal applicatios of cellulose-TiO2 coated cotton fabric
77
xvi
LIST OF TABLES
Table 1 Amount of cellulose coating on 4 g of cotton fabric 31 Table 2 Observation of antibacterial activity by AATCC 100 56 Table 3 Quantitatibe evaluation of bacterial reduction 57 Table 4 Evaluation of antibacterial testing by AATCC 147 57
Table 5 Estimated of cellulose fractions 64
Table 6 Spectrophotometric analysis of dyed sample 66
Table 7
Washing and Rubbing Fastness properties assessment of dyed samples
68
Table 8 Perspiration Fastness assessment of dyed samples 69
Table 9 Mechanical properties 71
xvii
LIST OF ABBREVIATIONS
AATCC American Association of Textile Chemists and Colorists ASTM American Standard Testing Methods
CB Conduction Band
CFU Colony-forming unit
CIE Commission Internationale de l'Elcairage DP Degree Of Polymerization
EC Escherichia Coli
FWHM Full Width Half Maximum
ISO International Organization for Standardization
KP Klebsiella Pneumonia
QAC Quaternary Ammonium Compounds
MRSA Methicillin-resistant Staphylococcus aureus MWCNT Multiwalled Carbon Nanotubes
PVA Polyvinyl Alcohol
PW6 Pigment White 6
ROS Reactive Oxygen Species
SA Staphylococcus Aureus
SEM Scanning Electron Microscopy SWCNT Singlewalled Carbon Nanotubes
UV Ultra Voilet
VB Valence Band
XRD X-Ray Diffraction
xviii
LIST OF UNITS
Nomenclature Unit
Air Permeablity l/m2/s
Bacterial/fungal concentration CFU/ml
Breaking force N
Cellulose content %
Colour intensity (IamgeJ) counts
Elongation %
Modulus Mpa
Porosity %
Relative colour strength %
Stiffness N.m
Thickness mm
Water vapor permeability %
1
CHAPTER 1
INTRODUCTION
1.0 Prologue
This chapter briefly describes the interest in the use of functional nanoparticles coating on cotton. It goes further by revealing the statement of the problem.
1.1 Background
Cotton fibre is one of the most common natural and leading textile fibre due to its unique properties such as hydrophilicity, biodegradability, durability, good dyeability, and relatively low cost [1]. Despite the excellent properties of cotton fabrics, some characters like the inherently hydrophilic property, impotent antimicrobial activity, low strength and poor sensitivity to the UV light, confine their wide applications, especially in some high-end areas for medicine, personal healthcare, functional textile and self-cleaning [2-4]. Therefore, value addition to cotton by functionalization has generated considerable academic and industrial attention, not only due to their potential use in physical, thermal, biological and medical protection, but also to meet the constantly evolving demand from consumers for advanced materials. Self-cleaning fabric materials are a research area that has accumulated huge interest over the years. The original idea of self-cleaning textiles envisioned a scenario where tablecloths and men’s suits shrug off coffee, tea, wine and other stains; or where large awnings, tents and other architectural structures stay spotlessly clean without requiring any washing or cleaning. Due to the remarkable developments made in this field during the last few decades, the concept of self-cleaning widened to include apparel that cleanses itself of body odour, curtains that rid themselves of tobacco odours to stay ‘ever fresh’, and hospital sheets that disinfect themselves to reduce the incidence of cross infections[5].
A strategy that is commonly adopted for the purpose of self-cleaning is to modify the textile surface with photocatalytic nanoparticles such as Titanium dioxide (TiO2) and Zinc oxide (ZnO) [6, 7]. TiO2 as a cheap, nontoxic, highly efficient, stable, and ecologically friendly photo catalyst, has been proved to be an excellent catalyst in the degradation of organic pollutants [8]. Cotton fabric is widely used in the apparel and household fields because of its good hygroscopicity, moisture regain and heat-resistant quality [9]. However, because of its poor stiffness and crease recovery, its application is restricted in some situations. As a differential fabric, stiff cotton fabric is important to many industries, such as applications to suit jackets, curtains and luggage. For comfort in hot environment people prefer to have some distance
2 between skin and cloth and that why most of the Asian and African countries use stiff cotton fabric due to high temperature. Starch is mainly being used to make cotton fabric stiff.
However, it does not give permanent effect. Cellulose is not soluble in water so it can replace starch if it is coated on the surface.
Antibacterial activity is very interesting and demanding properties of cotton fabrics [10-13]. In recent years, the commercial market for antibacterial fibers has grown rapidly due to the increased need of consumers. Polymeric materials, such as cotton, wool and flax, provides an excellent substrate for bacteria growth because they are contaminated easily with microorganisms under the appropriate environmental conditions [14]. Microbial proliferation eventually causes damage to the fiber materials and induces human infections [15]. Nano particles like TiO2, ZnO, CuO, Ag, carbon nanotubes etc. show excellent antibacterial activity.
TiO2 is most environment-friendly [16] among all other nano particles and shows multifunctional ability, that‘s why it was selected for coating with cellulose. There are several methods and techniques researchers have introduced to make cotton fabric functional by coating nanoparticles on the surface, in-situ polymerization, depositing nanoparticles on the surface etc. However, these methods lacking in durability. To overcome with this proplem, the new route has been introduced herein to make cotton fabric multifunctional by coating cellulose-TiO2 nanoparticles on the surface of cotton fabric.
1.2 Research Problem
Self-cleaning and permanently stiff textiles are becoming important due to market demand, and broad research is being done in this area [5, 17, 18]. TiO2 can be applied on different substrates such as activated carbon, stainless steel and glass [19]. TiO2 shows extraordinary photocatalytic activity since it has a high sensitivity to light [20]. Nano TiO2 has the ability to decompose dye pollutant such as Acid Orange [21], Methylene Blue [22], C.I. Acid Blue-9 [23], Methyl Orange [24, 25], Ethyl violet dye [26], C.I. Reactive Red 2 [27] and photocatalytic decomposition of some air pollutants [28]. Recently some researches have coated TiO2 on cotton fabric by in-situ suspension polymerization with nano TiO2-acrylate copolymer [29] and functionalizing cotton fabric with nano sized TiO2 [30]. However, durability is major concern with these methods.
Starching is commonly used for increasing stiffness of cotton fabric by applying starch [31, 32] to them. Application of starch is widely used for increasing the bending rigidity of collars and sleeves of men’s shirts and the ruffles of girl’s petticoats. However, that notwithstanding,
3 the stiffness arising from starching isn’t permanent due to the fact that when the fabrics are washed, starch dissolves in water [33] therefore leading to loss of fabric stiffness, and hence a need to reapply starch after each washing cycle. Cellulose is insoluble in water, therefore coating fabrics with cellulose leads a lasting and permanent stiffness effect unlike starch which is soluble in water whose stiffness is temporary [34]. In recent years, researchers have been trying to make cotton fabric self-cleaning and antibacterial in different ways such as:
antibacterial finishing of cotton by microencapsulation[12], by synthesizing Photo bactericidal porphyrin-cellulose nanocrystals [35], Treating cotton fabric by SBA-15-NH2/polysiloxane hybrid containing tetracycline [36], plasma treatment and ZnO/Carboxymethyl chitosan composite finishing [37], self-cleaning by copper (II) porphyrin/ TiO2 visible-light photocatalytic system [20], coating with nano TiO2-acrylate copolymer [29], Nano TiO2
coating after treatment of cotton fabric with carboxylic acids such as oxalic, succinic, and adipic acids [38], functionalizing cotton fabric with p-BiOI/ n-TiO2 heterojunction [39], bleaching and cationized cotton using nanoTiO2 [10]. However, these methods do not give durable ability to kill bacteria’s.
Research elsewhere has utilized various cellulose coated substrates for various applications such as high oxygen barrier and targeted release properties cellulose [34, 40], extension of the shelf life of rainbow trout fillets [41], bioactive composite coating [42], wood coatings [43] for active packaging [44] etc. Cellulose does not melt before decomposition and is insoluble in common organic solvents. Cellulose is a highly stable compound and its stability is primarily attributed to strong intra- and intermolecular hydrogen bonding leading to a remarkably stable fibrillar structure [45]. Solvents like 60% Sulfuric acid (H2SO4) [46], Ionic Liquid [47, 48], N-Methylmorpholine N-oxide (NMMO)[49], Sodium hydroxide-carbon disulfide (NaOH- CS2) [50], Dimethyl acetate/ Lithium chloride (DMAc/ LiCl) [51] can readily dissolve cellulose. Thus, there is a scope for cellulose coating on cotton fabric after dissolution since both the molecules are same and there will be exchange of hydrogen bonding for permanent change. Due to interlinkage between coated celluose and cotton cellulose, coated cellulose will not be washed away unlike starch. Hypothesis is that cellulose can carry nanoparticles and hold for long duration after coating with help of hydrogen bonding between coated cellulose and cotton fabric cellulose.
Coating with cellulose-TiO2 addresses four main uses: self-cleaning, antibacterial, antifungal and stiffness. For coating cellulose-TiO2, Urea-Thiourea-NaOH solvent system and 60 % H2SO4 solution were selected for cellulose dissolution. Urea-Thiourea-NaOH solvent system dissolves cellulose directly at -12°C [52] and 60 % H2SO4 is powerful and has the ability to
4 breakdown cellulose chains directly. The Degree of Polymerization of cellulose decreases after dissolution in 60% H2SO4 [46]. This report, therefore, presents the findings of the investigation of the microstructural, self-cleaning, antimicrobial, stiffness and comfort properties of cellulose-TiO2 coated cotton fabric for possible applications.
5
CHAPTER 2
AIM AND OBJECTIVES
Overall aim of this study is to develop a cellulose-TiO2 coated cotton fabric and its characterization for organic stain degradation, inhibition efficiency against bacteria’s, disinfection of cotton fabric from fungal colonization, stiffness, mechanical properties, X-ray diffraction, durability of cellulose-TiO2 against washing and comfort properties such as air and water vapor permeability for multifunctional applications. Orange II dye and wine have been selected for investigation of self-cleaning propeties and ImageJ software has been used to analyze stain degradation under UV light. The bacterias such as Escherichia coli (EC), Klebsiella pneumonia (KP), Staphylococcus aureus (SA), Methicillin resistant staphylococcus aureus (MRSA) have been used to study antibacterial activity of coated fabric. X-ray diffraction patterns based simulation model was used to understand the effect of solvent on the structure of cellulose.
The specific objectives are as follows,
a) investigation of morphology of cellulose-TiO2 coated cotton fabric
b) investigation of photocatalytic self-cleaning ability by degradation of orange II dye and wine stain under UV light.
c) evaluation of antibacterial and antifungal properties of cellulose-TiO2 coated cotton fabric d) investigation of stiffness, mechanical and comfort properties of cellulose coated cotton
fabric
e) effect of cellulose coating on dyeing, colour strength and related parameter with reactive dyes
f) durability of cellulose-TiO2 coated cotton fabric against washing.
g) development of simulation method to quantify amount of cellulose I, II and amorphous content by X-ray diffraction.
6
CHAPTER 3
LITERATURE REVIEW
3.0 Prologue
This chapter gives a broad overview of the field of research, background, underlying theories and up-to-date research that has been made in the field. The reader will familiarize him/herself to the experimental procedures which follow in the next section.
3.1 Cotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus Gossypium in the family of Malvaceae. The fiber (figure 1) is almost pure cellulose. Under natural conditions, the cotton bolls will tend to increase the dispersal of the seeds. The plant is a shrub native to tropical and subtropical regions around the world, including the Americas, Africa, and India. The greatest diversity of wild cotton species is found in Mexico, followed by Australia and Africa [53].
Figure 1. Cotton bolls ready for harvest [54]
3.2 Functional cotton fabric
Cotton is one of the most abundant and widely used natural fibers on the Earth. Due its strong absorption capability, high specific surface, porous structure, biodegradabality and less cost,
7 use of cotton has been extended from wear to technical textiles [55-57]. However, some characters like the inherently hydrophilic property, impotent antimicrobial activity, low strength and poor sensitivity to the UV light, confine their wide applications, especially in some high-end areas for medicine, personal healthcare, functional textile and self-cleaning [2-4].
Therefore, value addition to cotton by functionalization has generated considerable academic and industrial attention, not only due to their potential use in physical, thermal, biological and medical protection, but also to meet the constantly evolving demand from consumers for advanced materials (figure 2). Apart from the esthetic purpose of cotton, the value-added cotton materials have become a basis for many industrial and technical applications [58-62].
Figure 2. Functional fabric [63]
3.3 Self-cleaning materials
In 1975 discovered the botanists Barthlott and Neinhuis from the University of Bonn the self- cleaning capability of the Lotus flower [64]. The scientists observed that Lotus flowers get rid of mud and dirt while unfolding their leaves in the morning [65]. So they examined the leave surface structure of the Lotus with a scanning electron microscope discovering a not as expected smooth but a very rough structure (10-9 nano and 10-6 micro). This rough structure
Functional fabric Spring and
Summer Cooling
Touch Anti odor
Anti bacterial Anti UV
Fall and Winter
Keep Warm Anti fungal
Self- cleaning Anti Static
Healthy Energy
Negative Ions
Far
Infrared
8 is responsible for the super hydrophobic ability of the leaves. The leave’s surface has a double layer structure first it is covered by little pimples (papillae) whereupon a layer of hydrophobic wax lies. The wax prevents raindrops from getting into the pimples interspaces resulting in only 2% – 3% of the drops surface being in contact with the leaf. Additional is the contact angle at which a liquid or vapor meets a solid surface responsible for the water-repellent.
Figure 3. Lotus effect [66]
The smaller the contact angle (<90°), the flatter the droplets and the wetter the surface (figure 3). The larger the contact angle (>90°) the less the area of contact between the liquid or vapor and the solid interface, leading to a closer to dry surface. The Lotus pimples create a contact angle of over 150° [67]. These effects reduces the strength of adhesion and vests the lotus flower with a super hydrophobic surface.As the Lotus effect has been introduced into Bionics it has found its way to commercial use. Today we can find the Lotus effect in the textile industry producing hydrophobic cloth. Other fields of use include glass, plastics, painted surfaces,
9 metals and ceramics and equipped with a hydrophobic ability these products outpace competitors [68].
After understanding the phenomenon, scientists start thinking how one can mimic this "Lotus effect" (figure 3) and apply Lotus effect to our daily technology. For example, raincoats and umbrella will perform much better if one can apply Lotus effect [67]. In addition, paints incorporating the Lotus effect could keep houses and buildings clean and dry. Self-cleaning textiles are becoming important due to market demand, and broad research is being done in this area. With the increase of environment protection awareness recently, issues of the environmental pollution have become major concerns. Among these issues, the water consuming and release of wastewater during washing of materials is very important. Self- cleaning materials have attracted increasing attention. For example, the self-cleaning cotton fabrics with a life cycle of 25–50 times of washing are a class of new products classified as intelligent fabrics. About 14 million meters/year of such kind of fabrics are demanded in European Union market [69]. There is an even larger potential market in the area of Asia and Pacific. One benefit of using these self-cleaning fabrics is the resource savings on cleaning such as water and chemicals. On the other hand, the lifetime of the fabrics can be prolonged because the continuous self-cleaning of fabrics decreases the washing times of them. Such an innovation was made by depositing thin films of photoactive component on the surface of fabric. At present, the main photoactive component of self-cleaning fabrics is nano TiO2 [70].
3.4 Antibacterial cotton fabric
Bacterial resistance to antibiotics is a significant public health challenge, as infections caused by antibiotic-resistant bacteria claim the lives of nearly 23,000 people each year in the United States alone [71]. Recently, textiles with antiviral activity or antibaterial activity have become extremely important in the health protection of human body. The antibacterial activity of textiles can be obtained through the antibacterial finishing of textile using antibacterial agents or by incorporating them into synthetic fibers during extrusion [72]. A single pathogen, Methicillin-resistant staphylococcus aureus (MRSA), is responsible for nearly half of these fatalities. MRSA has been linked to invasive diseases including pneumonia [73] and sepsis [74], that affect a diverse population of patients including individuals with a compromised immune system such as young children. While a powerful arsenal of antibiotics was once capable of treating Staphylococcus aureus (S. Aureus) based infections, clinical isolates of MRSA have emerged to numerous antibiotics, including agents of last resort such as linezolid
10 and vancomycin [75, 76]. Researcher elsewhere has developed the antibacterial textile materials by incorporating, coating, depositing, treating, functionalizing, modifying with nanomaterials such as Titanium dioxide, copper, silver etc nanoparticles. The number of antibacterial agents that are suitable for textile applications on the market has increased dramatically in the past decades.
The main antibacterial agents include metals or metal salts [77-79], quaternary ammonium compounds (QACs) [80, 81] polybiguanides, [82] N-halamine, [83] chitosan, [84, 85] and triclosan [86]. These antibacterial agents have expanded greatly the use of textiles in pharmaceutical, medical, engineering, agricultural and food industries. However, most of the antibacterial agents still have some disadvantages, which limit their applications greatly. For instance, the uptake and durability of metals in textiles are the two big problems of treatment for the metal antibacterial agents. Many heavy metals are even toxic to environment. The QACs also have some inherent weakness, such as leaching from the textiles, incompatibility with the anion surfactant [87]. Dow Corning Company had produced one kind of QACs antibacterial finishing agent with alkoxysilanes (AEM 5700) for covalently binding onto the textile surface, imparting durable antibacterial activity [88]. However, the antibacterial activity of these durable QACs was also decreased or even expired because of the absorption of dirt, deadly microorganisms or complex formation between the positively charged QACs and the negatively charged anionic detergent during repeated laundering. In addition, the low antibacterial activity to epiphyte and the weak light tolerance influences the applications of polybiguanides greatly.
The bacterial resistance to triclosan has been well-documented and is of great concern.
Triclosan has been banned in textiles and some other products by many countries because of its produced toxic polychlorinated dioxins upon exposure to sunlight. The chitosan tends to be environmentally friendly in the antibacterial applications. However, the antibacterial activity of chitosan is pH sensitive and limits to acidic conditions [89]. The chitosan also shows weak adhesion to cellulose fibers and is leached gradually from the fiber surface by repeated laundering. These disadvantages motivate researchers to actively explore new antibacterial agents and technologies for antibacterial textiles finishing. In addition, antibacterial efficiencies and durability, environmental friendliness, health, and safety are also important to the antibacterial agents. TiO2 shows excellent photocatalytic activity towards light and has ability kill bacteria, fugi and clean the surface of material [16, 17, 90].
11 3.5 Antifungal cotton fabric
Textile fabrics by virtue of their physicochemical characteristics and proximity to the human body are susceptible to microbial attack, as these provide large surface area and absorb moisture that aid microorganisms to grow, transfer and propagate infection. Ubiquitous microorganisms cover all surfaces in natural and artificial environments. Textiles are appealing materials for use in several medical applications, including hospital uniforms and linens;
prosthetic valves; and wound dressings [91]. Microorganisms can cause problems in textile raw materials, process chemicals, during wet textile treatments, in textile and textile product warehouses during transportation, and even during the everyday usage of textile products [92].
Fungi produce at least three enzymes (‘cellulase complex’) of extra cellular activity during growth on exoglucanase or ß-D-glucosydases cellulose, respectively to remove disaccharide units from the chain ends of endoglucanases or ß-D-glucanohydrolases cellulose, respectively.
And randomly break the ß-1,4 bonds of cellulose chains; the third component is ß-D- glucosidases, hydrolyzing cellobiose into glucose units, which are then used as a carbon source for fungal growth [93].
With the growing awareness about cleaner surroundings and healthy lifestyle, the demand for protective clothing has increased among consumers. This has created significant challenges for textile researchers and industrialists to address the issue through innovative ways.
Consequently, the competitive and textile market is globally witnessing a rapid growth in the development of technical textiles and their end-uses that have generated many opportunities for the application of innovative finishes. Textiles with an antimicrobial finish and improved functionality find a variety of applications such as health, hygiene, and medical products, apart from healthy clothing. Among all textile finishes, antimicrobial finishing has become a very promising, high-growth research area due to their potential to provide quality and safety benefits to different kinds of textile materials [94].
Natural colorants from plant sources have been recently discovered as novel agents in imparting multifunctional properties to textiles such as antimicrobial, insect repellent, deodorizing, and UV protective besides imparting attractive shades. Application of natural colorants offers promise in developing antimicrobial textiles for aesthetic, hygienic, and medical applications owing to the presence of potent bioactive phytochemicals in their extracts.
Substances and extracts isolated from different natural resources especially plants have always been a rich arsenal for controlling the fungal infections and spoilage. In the recent past, considerable research work has been undertaken on the application of natural dyes in coloration
12 and antimicrobial finishing of textiles around the globe and use of natural dyes for antimicrobial finishing of textiles has been widely reported[94].
On cotton fabric, fungal contamination starts on the cutting edge where the spores can easily reach the fibre’s lumen. Hyphaes sprout in the lumen and form a mycelium, which grows toward the fibre’s wall, causing its degradation. The damage caused by microorganisms becomes visible with changes on the textile or fibre surface, mostly in the form of de-coloration and stains; in most cases, these changes are followed by a typically musty smell. De-coloration is mainly caused by chemical reactions between metabolites secreted by the microorganism and finishing agents or dyes in the textile material. In many cases, this leads to the production of pigment-like substances. One promising innovation is to impart these textiles with antimicrobial properties. Noble metals such as copper, gold, and silver have broad-spectrum antimicrobial activity. For example, silver has several effects on microorganisms, including impeding the electron transport system and preventing DNA replication [93].
3.6 Stiff cotton fabric
Cotton fiber poor stiffness and crease recovery restricted its application in some situations. As a differential fabric, stiff cotton fabric is important to many industries, such as applications to suit jackets, curtains and luggage.Therefore, there are many reports on anti-crease finishing and stiffness finishing [9]. Starch, cyanaldehyde resin, urea formaldehyde resin, poly vinyl alcohol (PVA) and polyacrylate are widely used to improve stiffness of cotton fabric. The starch is being used for increasing the bending rigidity of collars and sleeves of men’s shirts and the ruffles of girl’s petticoats. However, such stiffness is not permanent, because starch dissolves in water during washing and the fabric loses its stiffness, resulting in the need to reapply starch after each laundering. Cotton fabric treated by starch slurry has poorer elasticity than the original fabric, and is not durable. Grafting of starch onto cotton fabric has been reported. Cotton fabric treated with PVA softens easily when exposed to heat, and is also not durable.
Cyanaldehyde resin and urea formaldehyde resin release formaldehyde, which is a health hazard, and the fabric strength decreases with these types of resin. In addition, the treated cotton fabric has a harsh feel, poor elasticity and high shrinkage rate. Polyacrylate is also applied to stiffness finishing of cotton. However, the finishing effect is inferior to that of cyanaldehyde resin. The treated cotton fabric is inelastic and has poor freezing resistance [95]. Currently, resin is always used as the stiffness agent for cotton fabric finishing. The stiffness agent is left
13 on the fabric; this increases health concerns. Thus, it is important to develop a finishing technique that can make cotton fabric stiff but leaves no auxiliary chemicals on the fabric to meet upmarket consumer demand [9].
3.7 Functional nanoparticles
Recent years have witnessed the rapid development of inorganic nanomaterials for medical applications. Within the broad field of nanotechnology, which has developed rapidly over the last two decades, colloidal nanoparticles containing primarily inorganic components (herein inorganic NPs) have emerged as rich and versatile systems whose specific properties aid in medicine, be it as novel therapeutics or diagnostic tools [96]. Nanotechnology, a high-tech science and technology rapidly developed in the late 1980s, has been widely used in many fields such as raw material, chemical, textile, medicine, traffic, energy and so on. In recent years, many dyeing and finishing auxiliaries with special function and new textiles with high effective function have been produced due to the nanotechnology application in textile industry [97]. Because of this biocidal activity, metals have been widely used for centuries as antimicrobial agents in agriculture, healthcare, and industry in general.
Chemical structures of some nanoparticles which is being commonly used for functionality of material such as Titanium dioxide (TiO2), Zinc oxide (ZnO), Copper oxide (CuO), Silver (Ag), Carbon nanotubes (Singlewalled carbon nanotubes (SWCNTs) are shown in figure 4. Metal, oxide, or salt compounds based on copper and silver are among the most widely applied antimicrobial agents in this context. However, the use of these metals in industrial applications presents several challenges associated with the nature of the metal itself. Consequently, one of their first applications was in the form of salt-based additives, for instance as silver nitrate, avoiding its highly expensive metal form [97]. TiO2 shows excellent photocatalytic activity towards light. TiO2 is most environment-friendly among all other nano particles [16]. TiO2 is being used to to apply on materials such as glass, ceramics, textile etc for self-cleaning application. It is even being used as a whitener. Nanoparticles of TiO2 is stable in alkali and alkaline medium at room temperature that is why it is easy to process. Also TiO2nanoparticles has ability to kill bactrias and fungi. Due to these multiapplication approach it was selcted for coating on cotton fabric.
14 (a) (b)
(c) (d)
(e) (f)
Figure 4. Functional nanomaterials a) Copper oxide b) Titanium dioxide c) Zinc oxide d) Silver oxide e) Single walled carbon nanotube f) Multi-walled carbon nanotube
15 3.7.1 Titanium dioxide
Titanium dioxide is the naturally occurring oxide of titanium. The chemical formula of titanium dioxide is TiO2. It is also known as titanium (IV) oxide or titania. When used as a pigment, it is called titanium white, Pigment White 6 (PW6), or CI 77891. It has a wide range of applications, from paint to sunscreen to food coloring [98]. When used as a food coloring, it has E number E171. World production in 2014 exceeded 9 million metric tons. Titanium dioxide (TiO2) exists as three different polymorphs; anatase, rutile and brookite [99].
Figure 5. Forms of Titanium dioxide [100]
The primary source and the most stable form of TiO2 is rutile. All three polymorphs can be readily synthesised in the laboratory and typically the metastable anatase and brookite will transform to the thermodynamically stable rutile upon calcination attemperatures exceeding
∼600°C [101]. In allthree forms, titanium (Ti4+) atoms are co-ordinated to six oxygen (O2−) atoms, forming TiO6 octahedra. Anatase is made up of corner (vertice) sharing octahedra which form (0 0 1) planes (figure 5) resulting in a tetragonal structure. In rutile the octahedra share edges at (0 0 1) planes to give a tetragonal structure (figure 5), and in brookite both edges and corners are shared to give an orthorhombic structure (figure 5).
Brookite
Anatase Rutile
16 3.7.2 Uses of Titanium dioxide
Titanium dioxide (TiO2) is the most widely used as a white pigment, for example in paints, food products, personal care products etc [98]. It has high brightness and a very high refractive index. The light passes through the crystal slowly and its path is substantially altered compared to air. If you have many small particles orientated in different directions, a high refractive index will lead to the scattering of light as not much light passes through. In lenses, high refractive index means high clarity and high polarising power. Titanium dioxide has a higher refractive index than diamond and there are only a few other substances that have a higher refractive index [102]. Cinnabar (mercury sulphide) is an example. Historically, cinnabar was used as a red pigment. In 2001, the first self-cleaning glass was brought onto the market. This type of glass is coated in a thin layer of transparent anatase. To make the coating, anatase is first combined with an organic complexing agent consisting of organic molecules which can act as ligands and bind to the titanium ion with co-ordinate bonds. This process is necessary to convert the titanium dioxide powder into a more soluble form so that it can be spread over the glass surface evenly. Once the coating is applied, the glass is heated to burn off the organic complexing agent, leaving the anatase coating.[103]
The cleaning process works in two phases;
Photocatalytic breaking down of dirt.
Washing off breakdown products when it rains.
The photocatalytic hydrophilic surfaces utilize sunlight/indoor light to decompose the dirt and other impurities [17]. TiO2 based photocatalysts have gained considerable attention as TiO2 exhibits significantly high physical and chemical stability, low cost, easy availability, low toxicity and excellent photo-activity [17]. In the presence of light of suitable energy (where, the energy of the excitation source is higher than the band-gap energy of the material), an electron (e−CB) is excited from valence band of TiO2 to the conduction band, generating a positive electron hole (h+VB) in the valence band (figure 6). The photoexcited electron (e−CB) can in turn recombine with the electron hole (h+VB) and reduce the overall efficiency of the photoprocess. The charge carriers, which can escape the charge-annihilation reaction, migrate to the surface, where the photoexcited electrons can reduce atmospheric oxygen to generate superoxide radicals (•O2–) or hydroperoxyl radicals (HO2•). The valence band hole can also oxidize surface adsorbed water or OH– and produce •OH. These reactive oxygen species (ROS) can convert organic pollutants into CO2 and water resulting in the cleaning of the surface. A major limitation in developing self-cleaning materials based on TiO2 is the wide band gap of
17 the semiconductor, limiting its absorption to the UV region of sunlight, which comprises only 3–5% of the solar spectrum. Due to this wide band gap, utility of pure TiO2 is restricted in fabrication of self-cleaning materials (e.g., glass and tiles) for outdoor application [17].
In photocatalysis, light of energy greater than the band gap of the semiconductor, excites an electron from the valence band to the conduction band (see figure 6). In the case of anatase TiO2, the band gap is 3.2 eV, therefore UV light ( ≤ 387 nm) is required. The absorption of a photon excites an electron to the conduction band (eCB−) generating a positive hole in the valence band (hVB+) (Eq. 1).
TiO2 + hv → TiO2 (hVB+ + eCB− )
(1) Charge carriers can be trapped as Ti4+ and O2− defect sites in the TiO2 lattice, or they can recombine, dissipating energy. Alternatively, the charge carriers can migrate to the catalyst surface and initiate redox reactions with adsorbates. Positive holes can oxidize OH− or water at the surface to produce •OH radicals (Eq. (2)) which, are extremely powerful oxidants [104].
Figure 6. Schematic illustration of various processes occurring after photoexcitation of pure TiO2 with UV light [104]
18 The hydroxyl radicals can subsequently oxidize organic species with mineralization producing mineral salts, CO2 and H2O (Eq.( 5)).
eCB− + hVB+→ energy (2)
H2O + hVB+→ •OH + H+ (3)
Electrons in the conduction band can be rapidly trapped by molecular oxygen adsorbed on the titania particle, which is reduced to form superoxide radical anion (•O2−) (Eq. (4)) that may further react with H+ to generate hydroperoxyl radical (•OOH) (Eq. (6)) and further electrochemical reduction yields H2O2 (Eq. (7)). These reactive oxygen species may also contribute to the oxidative pathways such as the degradation of a pollutant (Eqs. (8) and (9).
O2 + eCB − → • O2− (4)
•OH + pollutant → H2O + CO2
(5)
•O2− + H+→ •OOH (6)
•OOH + •OOH → H2O2 + O2
(7)
•O2− + pollutant → degradation products (8)
•OOH + pollutant → CO2 + H2O (9)
3.7.3 Photo induced hydrophilicity by Generation of light induced surface vacancies The initial and widely accepted mechanism for photo-induced hydrophilicity was proposed by Wang et al. which relies on the formation of surface defects upon UV light illumination [105].
Friction force microscopic studies suggested that UV irradiation resulted in a structural change at the TiO2 surface thereby influencing the interfacial force along the solid–liquid boundary and consequently changing the contact angle. The surface of TiO2 consists of five coordinated Ti atoms with the sixth position occupied by H2O or OH–. It is believed that UV irradiation creates oxygen vacancies at the two coordinated oxygen bridging sites at the surface, thereby
19 converting Ti4+ ions to Ti3+. These defects can in turn increase the affinity for hydroxyl ions formed by dissociation of chemisorbed water molecules and thereby forming hydrophilic domains (figure 7). Moreover, crystal planes (1 1 0) and (1 0 0) of rutile TiO2 with bridging oxygen sites showed higher efficiency for hydrophilic conversion compared to the planes such as (0 0 1) without bridging oxygen sites [106]. Atomic force microscopic study of UV- illuminated rutile TiO2 single crystal showed that TiO2 surface consists of microscopic hydrophilic and oleopholic domains, which are believed to generate capillary flow channels for oil and water.
Figure 7. Schematic representation of photo-induced hydrophilicity. Electrons reduce the Ti(IV)–Ti(III) state and thereby the oxygen atoms will be ejected (creation of oxygen vacancies). Oxygen vacancies will increase the affinity for water molecules and thereby
transforming the surface hydrophilic [17].
It was found that if the hydrophilic TiO2 material is stored in dark for a couple of days, the hydrophilic character gradually decrease due to slow replacement of the chemisorbed hydroxyl and water molecules by oxygen molecules from air. However, the hydrophilic nature of the surface can be retrieved by further UV illumination. Nakajima et al. demonstrated the photoinduced amphiphilic surface formation for polycrystalline anatase TiO2 thin films [107].
20 However, prolonged UV irradiation was shown to convert the surface into a hydrophilic–
oleophobic one, which is considered to be due to variation in the rate of hydrophilic conversion of TiO2 grains. Rutile TiO2 exhibited photoinduced surface hardness correlated with the conversion of hydrophilic surface. This photo-induced change in surface hardness has been attributed to surface volume expansion resulting from the increase in distance between the adjacent Ti atoms arising from the dissociative adsorption of water molecules upon UV exposure.
3.7.4 Mechanism of self-cleaning, antibacterial and antifungal by TiO2
Figure 8. Mechanism of self-cleaning, antibacterial and antifungal by TiO2 [108].
Figure 8 shows the mechanism of self-cleaning, antibacterial and antifungal by TiO2 under UV light. The titanium dioxide, in contact with water and oxygen molecules adsorbs some radiation with an intensity of energy that is larger than the characteristic band-gap. Electrons promoted from valence to conduction band create free electrons and electron holes’ pairs.
These pairs produce reactive oxygen species like superoxide anions, hydroxyl radicals, and hydrogen peroxide molecules, which can oxidize organic compounds. These radicals can also
21 kill bacteria, viruses, fungi, and algae [109-113]. It is believed that the main cause of the biocidal effect of TiO2 is a damage of the cell membrane[114] and its polyunsaturated phospholipids [115]. Titanium dioxide can be applied on various substrates like glass, stainless steel, textile materials, composites, activated carbon etc.
3.7.5 Methods to apply Titanium dioxide
There are different methods to incorporate TiO2 such as facile synthesis of casein-based TiO2
nanocomposite[116], Platinum (IV) chloride modified TiO2 and N-TiO2 coatings for self- cleaning cotton fabrics[117], TiO2 doped withSnO2 thin films preparation by sol-gel method[118], Slightly carboxymethylated cellulose supported TiO2 nanoparticles[119], finishing self-cleaning material on cotton fabric[120], coating of TiO2 on cementitious materials[121]. Cellulose molecule is very stable in nature due to its strong inter and intra molecular hydrogen bonding. Solvents such as Ionic liquids[48], 60% sulfuric acid[46], Sodium Hydroxide-Carbon disulfide solvent system, can disturb hydrogen bonding and dissolve cellulose. Cellulose can be coated on cotton fabric by roller padding after dissolving in solvent. Sodium Hydroxide-Urea-Thiourea and 60% sulfuric acid were chosen to prepare the cellulose solution. TiO2 nanoparticles were dispersed in the cellulose solution by stirring in order to coat on cotton fabric.
3.8 Starching
Starch is the major carbohydrate reserve in plant tubers and seed endosperm where it is found as granules [122] each typically containing several million amylopectin molecules accompanied by a much larger number of smaller amylose molecules. By far the largest source of starch is corn (maize) with other commonly used sources being wheat, potato, tapioca and rice. Amylopectin (without amylose) can be isolated from 'waxy' maize starch whereas amylose (without amylopectin) is best isolated after specifically hydrolyzing the amylopectin with pullulanase [123]. Genetic modification of starch crops has recently led to the development of starches with improved and targeted functionality. Starch consists of two types of molecules, amylose (figure 9) normally 20-30% and amylopectin ( figure 10) normally 70-80%. Both consist of polymers of α-D-glucose units in the 4C1 conformation. In amylose these are linked - (1->4)-, with the ring oxygen atoms all on the same side, whereas in amylopectin about one residue in every twenty or so is also linked - (1->6)- forming branch-points. The relative proportions of amylose to amylopectin and - (1->6)- branch-points both depend on the source
22 of the starch, for example, amylomaizes contain over 50% amylose whereas 'waxy' maize has almost none (~3%) [124].
Figure 9. Representative partial structure of amylose
Figure 10. Representative partial structure of amylopectin
